Lecture 7: Neuranatomy of White Matter

Question 1

What is the white matter composed of?

Answer 1

Axons of the neurons

It appears white because of the myeline

Question 2

How is the white matter organized?

Answer 2

• It is organized in bundles of fasciculi:
  
  • Commissural fibres
  • Projection fibres
  • Association fibres
• Each fasciculus has a name and is associated with a function depending on what it connects
  
  • Not random
• As the brain develops, some connections are formed and some removed

Question 3

What are the commissural fibres?

Answer 3

• Connection between the hemispheres
• Commissural fibres:
  
  • Corpus callosum
  • Anterior commissure
  • Posterior commissure
  • Hippocampal commissure

Question 4

The Corpus Callosum

Answer 4

• Largest commissural bundle
• Divided into 7 parts:
  
  • Rostrum
  • Genu
  • Rostral Body
  • Anterior Mid-body
  • Posterior Mid-body
  • Isthmus
  • Splenium

Question 5

What does the Rostrum in the CC connect to?

Answer 5

• Orbitofrontal areas
• Pre-frontal areas

Question 6

What does the Genu in the CC connect to?

Answer 6

• Obitofrontal areas
• Pre-frontal areas

Question 7

What does the Rostral Body in the CC connect to?

Answer 7

• Premotor and Supplementary motor areas

Question 8

What does the Anterior Mid-Body in the CC connect to?

Answer 8

• Sensori-motor areas

Question 9

What does the Posterior Mid-Body in the CC connect to?

Answer 9

• Parietal Areas

Question 10

What does the Isthmus in the CC connect to?

Answer 10

• Posterior Parietal
• Superior Temporal

Question 11

What does the Splenium in the CC connect to?

Answer 11

• Occipital area
• Inferior Temporal areas

Question 12

The Anterior Commissure

Answer 12

• AC
• Connects areas of the temporal cortex to the subcortical structures (amygdala) and olfactory bulbs

Question 13

What are association fibres?

Answer 13

• Fibres connecting different areas of the brain within a same hemisphere
• Intra-hemispheric
• Association fibres:
  
  • Superior Longitudinal Fasciculus (SLF)
  • Middle Longitudinal Fasciculus (MLF)
  • Inferior Longitudinal Fasciculus (ILF)
  • Fronto-Temporal Extreme Capsule Fasciculus
  • Arcuate Fasciculus
  • Uncinate Fasciculus
  • Inferior Fronto-Occipital Fasciculus (IFOF)

Question 14

Superior Longitudinal Fasciculus

Answer 14

• 3 branches: Purple, Green and Orange
• Parietal to Frontal areas

Question 15

Arcuate Fasciculus

Answer 15

• Yellow
• Frontal and posterior Temporal areas

Question 16

Middle Longitudinal Fasciculus

Answer 16

• Light Blue
• Parietal to Temporal

Question 17

Fronto-temporal Extreme Capsule Fasciculus

Answer 17

• Purple
• Frontal to anterior-mid temporal areas

Question 18

Uncinate Fasciculus

Answer 18

• yellow
• Orbitofrontal to anterior temporal areas

Question 19

Inferior Longitudinal Fasciculus

Answer 19

• green
• Occipito-temporal connections

Question 20

Inferior Fronto-occipital Fasciculus

IFOF

Answer 20

• red
• Occipito-frontal connections

Question 21

What are Projection Fibres?

Answer 21

• Connection between cortex and subcortical structures
• Projection fibres:
  
  • External capsule
  • Interior capsule

Question 22

External Capsule

Answer 22

• Motor cortex to putamen
• unidirectional

Question 23

Internal Capsule

Answer 23

• Cortex to subcortical structures
• Massive white matter highway
• bidirectional

Question 24

In the spinal cord which are the tracts that consists of white matter?

Answer 24

• Descending tract (motor pathway)
• Ascending tract (sensory pathway)